03/03/2025
By Ananya Mukherjee

Candidate Name: Ananya Mukherjee
Defense Date: Thursday, March 6, 2025
Time: 10 a.m. to 12 p.m.
Location: In person: Room TBD, Olney Hall
Zoom: please email Ananya Mukherjee for the meeting link (ananya_mukherjee@student.uml.edu)

Thesis Title: Constraining primordial non-Gaussianity with large-scale structure
Advisor: Nishant Agarwal, Ph.D., Department of Physics and Applied Physics, University of Massachusetts Lowell
Committee Members: Viktor Podolskiy, Ph.D., Department of Physics and Applied Physics, University of Massachusetts Lowell
Timothy Cook, Ph.D., Department of Physics and Applied Physics, University of Massachusetts Lowell

Abstract: The large-scale distribution of galaxies in the Universe is expected to provide the next-generation of constraints in cosmology. For example, it can be used to infer properties of the primordial perturbations that seeded cosmic structure as well as properties of dark energy and dark matter. This information is typically extracted from summary statistics such as the two point function (power spectrum) and three-point function (bispectrum) of galaxies. A nonzero galaxy bispectrum, in particular, is generated not only by non-Gaussianity in the spectrum of primordial perturbations, but also by nonlinear galaxy evolution, and one of the goals of this thesis is to disentangle these two effects. To this end, we first obtain expressions for the next-to-leading order galaxy power spectrum and leading order galaxy bispectrum in the presence of local primordial non-Gaussianity, nonlinear bias parameters, and line-of-sight dependent selection effects. We then perform a Fisher analysis to estimate the 1-sigma errors on seven key cosmological parameters — the angular diameter distance, Hubble parameter, and linear growth rate at a given redshift, the cold dark matter density, the tilt and running of the primordial power spectrum, and the local primordial non-Gaussianity parameter — for a Euclid-like survey. We find that while the constraining power of a power spectrum-only analysis is significantly weakened by nonlinear bias and selection effects, adding the galaxy bispectrum helps recover cosmological information and, in particular, yields an O(10) constraint on the local primordial non-Gaussianity parameter. This is competitive to the constraint obtained from the cosmic microwave background, showing that future galaxy surveys can indeed provide the next generation of constraints in cosmology, as long as we include next-to-leading order corrections and higher-order galaxy statistics in the analysis.